The present invention relates to the area of the improvement of air quality, in particular the improvement of respiratory air in living rooms and workrooms by the use of absorber materials which are capable of reducing the contamination of the air by undesired odorants. In particular, the invention relates to sheet-like absorber materials having an air permeability which is suitable for the intended use, can be arranged on or in spatially limited, localized sources of undesired odours and ensure that the odours developed by these sources are bound and do not enter the respiratory air. In particular, the sheet-like absorber materials are intended for use in or on commodity articles or apparatuses, in particular technical apparatuses, for the household or other daily needs.
A field of use of the present invention which is to be singled out in particular is use in the interior of vacuum cleaners, where the dust which has already been sucked into the vacuum cleaner filter and continues to collect there over the time during which no change of filter is required constitutes a source of undesired odours. In the present Application, the purpose and the mode of action of the absorber materials according to the invention are therefore explained primarily for the example of a vacuum cleaner, but further potential uses for the absorber materials according to the invention, for example in the household, in the motor vehicle sector and other related areas, including healthcare, are evident to the person skilled in the art from these explanations and the following more briefly discussed further examples.
During vacuum cleaning, numerous constituents, for example crumbs and fragments of food constituents, particles from animal keeping, tobacco smoke, general house dust and microorganisms occurring in the environment to be cleaned, enter the vacuum cleaner filter bag together with the dust sucked in and either release odorants (“smell”) by their very nature or gradually decompose in the vacuum cleaner filter bag or rot there and as a result of such processes begin to produce an unpleasant smell. As long as the vacuum cleaner is not used, these odours remain substantially in the interior of the vacuum cleaner and generally do not greatly contaminate the room air. However, if the vacuum cleaner is put into operation again, these odours, together with their carrier atmosphere, are displaced from the filter bag by the external air sucked in and are blown out of the vacuum cleaner. It is for this reason that, when the vacuum cleaner is put into operation again, the result is frequently the release of a cloud of unpleasant odour, which is felt by many to be annoying and, for example, may make it necessary to thoroughly ventilate the freshly vacuumed premises after vacuum cleaning.
In view of this unpleasant phenomenon, there have already been various proposals to prevent or at least to reduce the odour development described by preventing the odorants from being blown out of the vacuum cleaner, so that they do not enter the room air. Thus, for example, DE 195 13 658 A1 proposes arranging, in a vacuum cleaner, behind the dust filter and before the turbine which blows the air sucked in by it through the filter out of the vacuum cleaner, a particular odour filter which is designed as an air-permeable support having an abrasion-resistant form of active carbon bound to the support. In this proposal, however, the odour filter comes into contact with the air to be purified only when the latter is sucked as an air stream through the filter. When the vacuum cleaner is switched on, the filter is therefore abruptly flooded by an odour cloud from the filter interior, which cloud has passed through the filter within a short time, and it has proved to be difficult to achieve satisfactory removal of odour from the moving air stream in the relatively short contact time.
According to DE 196 15 209 C1 and further documents discussed in the introduction of DE 196 15 209 C1, it was therefore also proposed not to remove the odours from a vacuum cleaner bag from the flowing exhaust air during operation of the vacuum cleaner but to ensure that they are bound by an absorber material from a static atmosphere when the vacuum cleaner is not in operation. For this purpose, however, the absorber material intended in each case must be in direct contact with the atmosphere in the interior of the dust filter even when the vacuum cleaner is not switched on, so that it can prevent this atmosphere from becoming saturated with the undesired odours at all. The proposed absorber material is a filter paper which is impregnated at least on one side with solid adsorber particles and which is used in combination with a particle filter. Materials based on active carbon and natural or synthetic zeolites are mentioned as adsorber particles. In the case of the proposal according to DE 196 15 209 C1, however, discharge of the adsorber particles from the treated layer and hence blockage of the following particle filtration layer may occur owing to mechanical loads, which results in decreasing air permeability of the filter and hence a reduced duration of use. Furthermore, a discharge of the adsorber particles from the bag can never be completely prevented, resulting in contamination of the air actually to be freed from particles. Moreover, the adsorption capacity in the filter bag is gradually further reduced by the adsorber loss.
A related reference is mentioned below for the sake of completeness and is concerned with effectively eliminating odours of sucked-in dirt before the air is blown out in the region of the dust filter bag. Thus, it was also proposed to place active carbon in additional specially produced filter cassettes in the air stream of the vacuum cleaner (cf. DE 42 40 172, DE 42 04 553), with the disadvantages that the suction power suffers through these additional assemblies and odour adsorption takes place only during the operation of the vacuum cleaner owing to the spatial separation of odour source and odour adsorber.
WO 00/40134 proposes arranging the adsorber loosely or in a three-dimensional framework structure (e.g. foam) in a layer of a multilayer filtration medium. In particular, the poor handling during the production of the medium should be mentioned as disadvantageous here (dust generation, trickling, non-uniform distribution due to shaking, the presence of a separation layer or on connection of layers by welding or adhesive bonding).
DE 195 31 343 describes a method in which the odour-adsorbing element is arranged spatially separately from, but in the immediate vicinity of, the dust bag. Here, the inconvenient handling during changing of filter elements should be noted since the capacities of two separate components may be exhausted at different times. Thus, constant checking of the operability is expedient. Functioning is guaranteed only with active flow through the element when the vacuum cleaner is switched on, whereas the adsorption is prevented in rest phases owing to the spatial separation.
In addition to active carbon particles, particulate zeolites are also employed for uses of the type mentioned. Thus, for example, EP 1 674 014 A1 proposes the use of, in particular, zeolite particles in immobilized form on that layer of a multilayer filter which is outermost on the outflow side. However, a disadvantage of the use of zeolites is in general their high selectivity and hence limited binding capability for various constituents of an odour, which as a rule is a complex mixture of different odorants, and the reversibility of the odour adsorption, together with the abrasive effect of the zeolite particles in the production process and during later processing steps.
With the use of particulate adsorbers, the immobilization of these substances is generally problematic since fixing of the particles on a support material, for example by an adhesive, can lead to loss of the adsorption capacity since there is the danger of sealing the surface of the particles.
The adsorber materials (active carbon, zeolites) discussed so far belong to a type of materials which, owing to a large adsorptive free surface area, substantially adsorptively bind odorants to be removed from the gas space, for example to their internal surface, for example in the zeolite crystal lattice, or in their pores (mesopores or micropores, for example of active carbon). The so-called cyclodextrins constitute a further class of substances having a comparable principle of action.
However, materials of said type, particularly when they are used alone, have a number of shortcomings which make them appear a suboptimal choice:
Active carbon is preferred for applications in which a broad action spectrum, high capacities and good kinetics are important. A disadvantage is a certain reversibility of the adsorptive binding which manifests itself, for example, as a tendency to result in desorption of the previously adsorbed odorants on high saturation of capacity, and a tendency that competitive displacement of adsorbed molecules by others which have a higher affinity for the surface of the active carbon is observable. In particular, aromatic hydrocarbons (benzene, toluene, xylene, abbreviated to BTX) compete with other molecules for free surfaces on the active carbon. Owing to their brittleness and black colour, moreover, their use is limited to areas where mechanical tolerance and surface appearance are not important.
Depending on the exact crystal structure in each case, the class consisting of the zeolites has a high adsorption specificity. Depending on the ratio of silicon to aluminium in the crystal structure, more or less pronounced hydrophilic properties are obtained in the cavities of the crystal lattice. As a result of the pronounced selectivity with respect to the polarity of the guest molecule, there is a high probability of competitive displacement from the host lattice. Zeolites are as a rule colourless but, being hard granular particles, are not suitable for all application forms.
Cyclodextrins, owing to their molecular form, in which the hydrophilic OH groups of the sugar base units point outwards and a hydrophobic region forms in the cavity, have a narrower action spectrum especially for lipophilic molecules and slower adsorption kinetics. In addition, with them as with active carbon or the zeolites, desorption occurs due to competitive displacement or elution.
What has been explained in the present Application so far with reference to the conditions in a vacuum cleaner also applies more or less to other areas of daily life where undesired odours develop. Thus, undesired odours or odour-saturated static gas spaces (odour-saturated stationary atmospheres) are also present elsewhere, for example in other more or less closed waste containers, e.g. dustbins, containers with medical waste, containers with food residues and the like, shoes, from which they can suddenly emerge and enter the room air on opening of the containers. Odour-laden relatively closed atmospheres also develop in narrow confines having a high density of occupation by persons and/or animals, for example, in the interior of vehicles, in transport rooms, and may also be present, for example, inside technical apparatuses, for example those with air cooling. Odour absorption from odour-laden closed atmospheres, without substantial air exchange with the surrounding atmosphere is to be regarded as “static” even when such an atmosphere is circulated to intensify contact with the absorber. An odour-laden microclimate in which odours propagate and concentrate can also form in the vicinity of odour extractors or extractor hoods for kitchen odours. Unless, in the respective individual case, the person skilled in the art is prevented from applying the teaching of the present invention for particular, case-specific reasons, this teaching can also be applied to other fields of use of this type, i.e. outside the narrow range of air improvement in vacuum cleaning, without their being any need to expressly list all possible individual cases herein.
It is evident from the abovementioned description of the prior art that there is still a need for an effective reduction of the contamination of respiratory air or room air by undesired odours from various apparatuses and articles of the household or of daily needs, for which a vacuum cleaner is an important example.